Manufacture of tetraalkyllead compounds



April 14, 1953 TANNER 2,635,107

MANUFACTURE OF TETRAALKYLLEAD COMPOUNDS Filed Nov. 10, 1952 s Sheets-Sheet 1 INVENTOR.

HOMER M. TANNER AQMW April 14, 1953 H. M. TANNER 2,635,107

MANUFACTURE OF TETRAALKYLLEAD COMPOUNDS 7 Filed Nov. 10, 1952 3 Sheets-Sheet 2 FIGURE 2 INVENTOR.

HOMER M. TANNER ATTORNEY April 14, 1953 H. M. TANNER 2,635,107

MANUFACTURE OF TETRAALKYLLEAD COMPOUNDS Filed Nov. 10, 1952 5 Sheets-Sheet 5 FIGURE 3 JNVENTOR. HOMER M. TANNER BY I ATTORNEY Patented Apr. 14, 1953 MANUFACTURE OF TETRAALKYLLEAD COMPOUNDS Homer M. Tanne Ba Rou 133: ass en to Ethyl C p ration, N w York, .N. Y a corporation of Delaware Application November 10, 1952, Serial No. 319,633 8 Cl ms (o1. Jason-4,437)

s n n o relates to an improved method o m ufacturing tetraalhy lead comp undsre p t la y. h inv n ion re ates t the p o u t on f tetraalkvllead compounds by the treatment of a odium-lead a oy with a liquid a ky atine a ent, and to the m nufa ture of such alloy in a new and improved super-reactive solid form. The present application is a continuationv -nart of my pr or appl cati ns Seria :No 182,617, filed August 31, 1950, and Seri l No. 188,395, filed October 4, 1950. The tetraallgyl derivatives of lead are of .commercial importance, especia ly tetraethyllead, which is widely used as an antiknock additive in gasoline, p p r b a t ng mono d-iin e d alloy with l qu d t yl ide a a em e a ure of ov 70 C. In carrying out this prior process, sodium and lead were mixed in the liquid phaseand then solidified as a large slab of solid alloy. This slab was then comrninuted or ground to particles predominantly in the 4 to 16 mesh screen size range. Such comminuted alloy and liquid ethyl chloride were then reacted in a closed autoclave with agitation, according to the reaction of unreacted sodium. The above described process therefore is limited :ifQr ,most practical nure poses to batchwise operations wherein, a residence time of several hours is permissible.

An object of the invention is to increase the rate of alkylation of lead to tetraalkyllead compounds, especially -;te traethyllea d. Another ob- .iectis to reduce he reaction period .or residence time required the alkylation formation of 'tetraal y lead compounds with equ va'1e t or in:-

creased yields over .those formerly obtained.

other object is "to provide a process particularly suited for continuous operation characterized :by

relatively short residence periods.

,Additional objects of :my invention are to pro- =vide a method ;for the continuous manufacture of a highly reactive alloy/comprising sodium and lead. Yet another object is gto provide a method and a paratus whereby the am unt .01 operatin .laboris substantial y reduced- .Another obj c i t nro fidwei apparatus andamemod'wheheby l ke 455 m 'ilhkfil iwii hiti fifi i i e lila shape,theusual Tetraethyllead has been vcommercially possi i ities of exposure of the alloy to moisture and air are greatly minimized. .Still another object is to min mi e or s b ta ially mi a formation of dusts or fines.

The invent on inc udes. the dep i herine o a thin layer of m t n a y on a d, ota in tal ur a e w teb e wi h id o and the cooling of the alloy to the solidification temperature under conditions such that the outer w i en is c racte iz d by the pr o a e f n iee s natural aces o i entifia e crystals- By id ntifiab e c s als i m ant ta s ming those de os te rom a supe t solution in that the natural orientation of adjaent cr stal fac s of disc ete c y a are c r y evident, According tn the present invention, a large proportion of the alloy exists in the form of ch i en ifiable c st s in o t he i t ax a mens n 2 6 CIYSW S e n an a eciable fraction of the thickness of the alloy. In contrast, in the conventional method for alloy manufacture, he bulk of the alloy is relatively slowly solidified, under conditions conducive to the -slow formation of massive crystals. Further, the .comminuting of the conventional alloy results in the iormation of a large amount of fractured, irregular surfaces rather than the naturally occurring crystal faces characterizing alloy pro.- ;duced according to the present method. The alloy so produced, being in the form of thin dustfree flakes characterized by having at least one Iace comprising predominantly projecting nat- ,ural faces of identifiable ,orystals, is then alloyifated according :to the present invention with an excess of liquid allrylating agent.

The alloy :for the process can ,be produced by a variety of methods. In general, the preparation ,of the alloy is characterized .by the quick-chilled solidification of athin layer .of molten alloy, with fit least one side of the layer exposed to an inert gas. A preferred method of preparing ,the alloys by process involving the deposition or adhesion o a t a e oi ah nnota coo e metal ur a e wh ch i -;p e creh v an a o con n an an recia le amount o op er. u h as time. e is re ed ith one the meta r a a airly ra d r e such tha th a o is s fied and oo ed t a tem r tur ap r c ably below i ssoli ii a on tem er ture i .a .brief nericd. A P e er e oocl nsra e nrov cles for sub-Coolin the t ny c o a y tc a tempera re of about .or more below {the S.Q1 idi-fi catio n temperature F n h :PQHQSi-Q ro none .to six seconds. The alloy is then parted from the metal surface and broken 3 maximum dimension of the flakes being from about A; to /4 inch.

Various reaction or alkylation techniques can be utilized as desired in carrying out the ethylation. Among the reaction techniques which can be utilized are the conventional batch operation, wherein a charge of alloy is alkylated in a heated stirred autoclave. The process is, however, peculiarly suited for continuous processing because of the increase in rapidity of the alkylation which is obtained. In an important embodiment of the process for continuous manufacture of tetraethyllead, ethyl chloride and flakes of monosodium-lead alloy manufactured as generally described above, are fed to the base of a vertically positioned cylindrical reactor. The ethyl chloride is used in substantial. excess, suitable proportions for this embodiment being of the order of 20 to 30 parts of ethyl chloride to one of monosodium-lead alloy. The reactor is maintained at an elevated temperature, from about 70 C. to 100 C.,'by means of the heat evolved during the reaction. The flow rates of materials are adjusted according to the size of the reactor to provide a residence time of the order of 5 to 30 minutes. The alloy particles start reacting immediately upon exposure to the elevated temperature reaction conditions, and as a result of reacting, break down into fine particles. These particles are transported upwardly by the flow of ethyl chloride and tetraethyllead produced by the reaction. The reacted materials and products are discharged from the reaction vessel'and the residue of solids is removed from the liquid phase by known mechanical operations, following which the tetraethyllead is recovered from the liquid phase.

Many embodiments of the invention are possible, both with respect to the chemical analysis of the alloy employed and also With respect to the apparatus utilized. Thus a series of sodium-lead alloys of variable sodium content can be produced according to the process. In the apparatus employed, numerous metals can be used for the rotatable metal cooling surface, providing only that it is wettable with the molten a1 loy. In a preferred embodiment, an alloy consisting of a monosodium-lead composition, NaPb, is deposited in a thin layer of about 0.01 to 0.05 inch in mean thickness on a cuprous metal surface, the solidification and cooling time being limited to from about 1 to about 6 seconds. Minor amounts of other alkali metals, for example up to about 5 weight per cent potassium, can be substituted for a portion of the sodium content of the alloy and similar benefits of the invention are obtained.

The details of the method of the invention and of apparatus used for making the alloy will be more easily understood from the accompanying figures and from the examples hereafter given. Figure 1 is an elevational view of a preferred embodiment of apparatus, comprising a casting drum, a molten alloy supply vessel, disengaging means and supplementary comminuting means, plus a containing enclosure making possible the full exclusion of the atmosphere and moisture. Figure 2 isa photomicrograph of a typical specimen of the super-reactive alloy produced according to my method, showing the preponderance of natural intersecting crystal faces in the alloy. Figure 3 is a photomicrograph of alloy produced by conventional means in the so-called massive form.

Referring to Figure 1, this is a schematic secdrum l2.

420 C. by heating element l9.

4. tional elevation of a preferred apparatus for the process. The main elements of the apparatus are a molten alloy supply tank ll, a rotating drum l2, a tangential parting blade 13, a breaker roll M, a discharge section I5 for the solidified alloy and a totally enclosing envelope or cover IE. Supplementary or auxiliary equipment for implementing continuous operation includes a heated feed line 57 for additional alloy, and heating elements !8 and H) for supplying heat to the alloy supply line and supply tank. Such heating elements include a fuel gas supply line, a burning head, and venting means or flues. Lines 20 and 2| are supply and discharge lines for providing a circulation or a steady supply of a dry inert gas, for example nitrogen, argon, or helium.

Drum I2 is mounted and rotated on a hollow shaft 22 which also acts as a conduit for a cooling fiuid supplied uniformly to the interior of the The cylindrical surface of the drum is preferably of a "cuprous metal, the end faces being normally and preferably fabricated of a ferrous alloy, relatively non-wettable with molten alloy. Several rows of pins 23 are mounted on or attached to the drum surface, being spaced at intervals of approximately 3 inches along a surface line parallel to the drum axis. The pins 23 are preferably made of a metal appreciably less wettable than the drum surface, for example,

stainless steel or other predominantly ferrous metal.

The parting blade i3 is tangentially located close to the drum surface at a point at which the alloy is entirely solidified and uniformly cooled to the preferred temperature. The parting blade I3 is fabricated with a number of notches or gaps which'coincide with the position of pins 23.

The alloy parted from the surface of the drum l2 by blade 13 passes over said blade as relatively large flakes or cards of solid alloy and falls to breaker plate 24. The breaker roll M rotates, the pins 25 passing through notches in the breaker plates 24 and comminuting the cast alloy into irregularly shaped small flakes with maximum dimensions of about to A inch. The broken or comminuted alloy collects in hopper l5 and is discharged to a portable bin 23 through valve 26. The portable bin 28 is also fitted with a slide valve 2? to allow protection of the super-reactive alloy contents against atmospheric oxygen and moisture during transport. The bin 28 is attached to the hopper I5 by connection with flange 29.

The following detailed working example describes the manufacture of monosodium-lead alloy in the above described'embodiment according to the method of the invention.

Example I 7 A supply'of molten monosodium alloy was introduced through feed line I? to feed pan H, and was maintainedat a temperature of about In the forming operatiomdrum E2 was rotated at a peripheral speed of 0.26 feetper second. The molten alloy was maintained at a depth providing an immersion time of approximately 0.9 second. The heat of solidification was removed by cooling water supplied to the drum interior through the bearing shaft 22, the average temperature of the cooling water being about 30 C.

The solidified alloy upon-{reaching the position of the parting blade I3 was cooled to C.,

approximately 220 C.- -b'elow the melting point.

At emperature theiall y is f ly solidified and partially-freed'from the surface of the drum I2. The parting blade therefore served primarily to guide the alloy sheet to the breaker plate 24.

The action of the breaker roll 14. and pins 25 comminuted the alloy to irregularlyshaped chips or flakes. with'a maximum dimension of to inch.

The flakes or chips 01'- alloy had a mean thick.- ness of about One-inch, and were free of dusts or powders. I I

The characteristics of the alloy produced according to the above working example is illus-.- trated by Figure 2, which is a photomicrograph of the alloy surface, enlarged approximately 30 diameters. It will be noted from the figure that the surface consists predominantly of projecting natural crystal faces. These include adjacent faces forming the apexes of octahedral shaped crystals 3|, 32, 33, 34, 35, 36 oriented at substantially right angles to the main plane of the alloy surface. In addition, there are numerous equilateral triangle faces 31, 38, 39, Ml which are oriented substantially parallel to the main plane of alloy surface. Even in these instances, however, the crystal faces project above the mean surface of the alloy flake. Comparison of the dimensions of the crystal faces with the mean thickness of the alloy shows that the axial dimension of the octahedral shaped crystals, whose projecting faces form thesurface of the alloy, is-usually in the range of 10 to 50 percent of the mean thickness of the alloy. In the case of the thinner forms of reactive alloy, the crystal dimensions frequently are above this range.

The significant attributes of the alloyof the present invention are further apparent by contrast with the appearance of conventionally prepared alloy as shown by Figure 3-. This figure is a photomicrograph of monosodium-lead alloy cast in conventional manner; in thick section. As with the super-reactive alloy illustrated by Figure' 2,. Figure 3 is also an enlargement of 30 diameters. It will be noted that the alloy is characterized by the substantial absence of projecting natural crystal faces having a precise orientation to the adjacent and intersecting crystal faces. In contrast the surface is composed of large segments of irregular shape, apparently representing the termini: of massive crystals which form or grow slowly from the cooling surface. As heretofore explained; comminution of suchmassive alloy results in the fracture of such massive crystals and the formation of irregular surfaces which are evidently, less reactive. than the natural crystal faces of the improved alloy.

As previously stated, an outstanding attribute of the alloys of, the invention are their super,- reactive character in being alkylated to form tetraalkyllead compounds. This attribute. is of particular benefit for application to a. continuous alkylation process, in that it provides a high degree of reaction with shorter residence times than previously considered essential, The alloy is also of course, beneficial in batch operations, which previously were characterized by residence times. r rea per ds of several urs. or

more.

The following examples illustrate the signifi cant improvements obtained by the process; for a full understanding of the advantages of the method. All. the yields cited in the following alkylation examples are based on the sodium content of the alloy. r I

6 Example I'l' 100 parts of flaked monosodium-lead alloy was sealed in a container of thin. glass, and carefully inserted in a reaction vessel. The alloy flakes had a mean thickness ofabout 0.01 inch and were characterizedby having one face consisting predominantly of natural crystal faces of octahedral crystals projecting from the mean elevation. 211 parts of ethyl chloride were then added and the reaction vessel was tightly sealed. The reactor-and the charge were heated to C. and the alloy exposed to the ethyl chloride by breaking the glassenveloper or container, this being accomplished by causing a steel ball previously inserteel in the reactor-"to drop and break the glass; The reactor and contents were maintained at 85 C; for exactly'five minutes; and the reactor was then immersed in a. cooling bathmaintained at a temperature-appreciably below 0 C., at which temperature no: reaction. occurs. The contents of. the reactor were then. removed and the tetraethyllead: recovered by leaching or extracting with benzene. 10.5 parts of tetraethyllead. were obtained. corresponding. to. a yield. of 30 per cent.

Example III The procedure of Example II was. repeated, except that the reaction was continued for: a period of 10 minutes; 24 parts oftetraethyllead were produced, corresponding to a yield of 68 per cent.

In order to illustrate the increased reaction rate and production achieved by the process, the foregoing examples. were. repeated, using conventional comminuted; alloy. The results are given in the. following examples.

Example IV parts of comminuted massive alloy; the alloy being in the. 4. to 1 6 mesh size range, and 211 parts of ethyl chloride, were reacted by the same procedure as in Example II, for a period of five minutes. Only 1.8 parts, oftetraethyllead were produced,corresponding, to a. yield of 5 per cent.

Example. V

The procedure of Example III was repeated, except thateomminuted. massive alloy was used. A reaction of 10. minutes produced 8.1- parts of tetraethyllead, corresponding to a yield of 23 per cent.

It will be evident from the foregoing examples that the present process results ina major increase in the production of t'etraethyllead which is possible with short residence-times. Thus, the production of tetraethyllead. is increased by a factor of 600 per cent forafive minute residence period, or a factor approximately 390- per cent with a residencetime of- IO minutes;

Theimproved process is beneficial without catalysts, as above described; and also results in additional improvements, with catalysts or accelerators known to the art. Catalysts which can beneficially be used in the process include the anhydrides of carboxylic acids,- as disclosed in U. S. Patent 2,426,598. Other catalysts include the non-quinoid'al ketones, ea g;, acetone (U. s. 2,464,391), esters ofcarboxylic'acids (-U; s. 2,46 i,398)-, amides (U. S. 2,464,399), acetal's- (U. S. 2,477,465) and aliphatic aldehydes (U. S. 2,51 2 Thefollowing examples illustrate the results obtained by my processwhenacatalyst is utilized therein.

Example VI 100 parts of monosodium-lead alloy, in the form of reactive flakes of about 0.01 inch mean thickness, and having maximum dimensions of from A; to inch, and 211 parts of ethyl chloride were added to a reaction vessel. As catalyst, approximately 1.5 parts of acetone was also introduced. The reaction vessel was closed and immediately heated to 85 C. and maintained at that temperature for five minutes with agitation. On completion of the five minute residence period, the reaction vessel and contents were immediately quench cooled to below C. The tetraethyllead was then separated from the reaction products, as heretofore described, and measured. 27.4 parts of tetraethyllead were produced by the reaction, corresponding to a yield of 78 per cent.

Example VII This example illustrates the production which is realized at a residence time of 10 minutes. The procedure described in Example VI was repeated except that the residence time was increased to 10 minutes. 29 parts of tetraethyllead were produced, corresponding to a yield of 82 per cent.

For contrast of the above results obtained with the use of a catalyst in the present process, the following examples show the typical yields which can be realized according to the conventional process.

Example VI II 100 parts of comminuted massive alloy and 211 parts of ethyl chloride were reacted in the manner already described, in the presence of about 1.5 parts of acetone. The reaction, with a residence time of five minutes, produced 23.6 parts of tetraethyllead, corresponding to a yield of 67 per cent.

Example IX The procedure of Example VIII was repeated, except that the residence time was increased to 10 minutes. 27.4 parts of tetraethyllead were produced, corresponding to a yield of '78 per cent.

The improvement efiected by the present process, in comparison with the former method, is evident from the above examples given in the presence of highly effective catalysts. Thus, the present process, provides a sixteen per cent increase in production with a five minute residence time, and a five per cent increase with a ten minute residence time.

In addition to the immediately obvious advantages apparent from the foregoing examples, comprising the increase in production possible at brief residence periods, other important advantages are obtained. Thus, an equally significant improvement is obtained with respect to the reduction in time achieved without decreasing the yield. This improvement is illustrated by the following examples.

Example X 100 parts of flake monosodium-lead alloy and 2500 parts of ethyl chloride were reacted at 85 C. in the presence of 1.5 parts of acetone. The reaction was carried out in an internally agitated reactor. Provision was made for withdrawing samples of the liquid phase during progress of the reaction. These samples allowed following the course of the ethylation. Determination of the amount of tetraethyllead formed during the ethylation showed that a yield of about 85 per cent was obtained in ten minutes, further yield being at a very low, almost imperceptible rate.

Example XI The procedure of foregoing Example X was repeated, except that conventionally prepared alloy was utilized. In this reaction, thirty minutes were required to attain a yield of 85 per cent, or a residence period greater by a factor of 300 per cent times the residence period necessary by the improved process.

The reasons for the improved results eifected by the process are not precisely understood. It is believed, that the reactivity of the alloy is an attribute imparted by the preponderance of projecting natural crystal faces which characterizes the reactive alloy employed. It was first theorized that the increase in reactivity was because sodium-lead alloy in the flake form, merely had more actual surface than previously used alloy particles. This supposition was disproved, however, by the discovery that comminuting reactive flake alloy to a fine powder, thereby greatly increasing the surface available for reaction, results in a substantial decrease in activity. Thus, when the yield of tetraethyllead obtained by ethylating a flake alloy was '78 per cent, the yield obtained by ethylating the same alloy, which had been ground to a powder passing a 50 mesh screen, was only 59 per cent. It was therefore concluded that the reaction rate obtainable with the flake alloy is a unique property which cannot be ascribed solely to the extent of the alloy surface but instead is a characteristic of the particular form of the alloy.

The mean thickness of the alloy can be varied widely without adversely affecting the beneficial results of the process. By mean thickness is meant the thickness calculated from the area, weight and density of the sodium-lead alloy. Thus, alloy ranging in mean thickness from about 0.008 to about 0.12 inch mean thickness has been found fully satisfactory. The preferred range of mean thickness is from 0.01 to 0.05 inch. Flakes of less thickness are difficult to produce. Flakes thicker than this range, while perfectly satisfactory with respect to reactivity, are less convenient to handle and feed into reactors because they exhibit a tendency to break into relatively large fragments in production.

The most important embodiment of the process involves the ethylation of monosodium-lead alloy, NaPb, to produce tetraethyllead. However, the process is readily utilized in ethylation of other alloys of sodium and lead. For example, alloys having the composition NazPb, NagPbi and NalPb, can be effectively used. Normally, alloys consisting substantially only of sodium and lead are produced and alkylated, but if desired a small proportion of the sodium content can be substituted by potassium metal. In addition, it will be understood that minute traces of other metallic impurities sometimes found in commercial lead may be present in the alloy as in other alkylation processes. In addition to this series of sodium-lead alloys, the process can utilize other alkylating agents. Typical examples of other alkylating materials are methyl chloride, methyl bromide, ethyl bromide or iodide, diethyl sulfate, isopropyl bromide, and others.

Substantial variation in the apparatus for preparing super-reactive alloy is permissible. The rotatable surface or drum upon which a layer of alloy is adhered and solidified according' to the process is, fabricated of a metal which is wettable with the moltenalloy. The cuprous bearing metals are preferred forthis service, as they are easily wetted with sodium-lead alloys. The term cuprous bearing metals refers to copper itself and to the numerous alloys of copper containing about per cent or more copper. The preferred metals for this service are alloys containing at least 60 per cent copper. Among the metals which have been satisfactorilyused for the rotatable surface are Monel metal per cent copper), yellow brass containing 65 per cent copper and percent zinc, Admiralty bronze (71 per cent copper, 28 per cent zinc, 1 per cent tin), and Everdur bronze (96 per cent copper, 3 per cent silicon). All the above have the property of being wettable with sodium-lead alloys as required for the process. The process is not restricted to cuprous metals, however, although they are preferred in most instances. It has also been discovered that silver is satisfactorily wettable, but its use will ordinarily be avoided. because of the relatively high cost. Ferrous metals are not precluded from this service, and can be utilized. In general, higher operating temperatures are required to cause molten alloy to adhere to ferrous metals, and mechanical arrangements are more usually required. to provide retention of solidified alloy on the rotatable surface until the alloy is removed. It is helpful, particularly in the case of a rotating surface of ferrous metal, to knurl or otherwise roughen the metal surface.

As heretofore indicated, it is preferred that the solidified alloy'layer the sub cooled to about 200 C. below the solidifying temperature before removal or parting from the rotating metal surface. This discharge condition has been found to provide several advantageous results. Even though alloy has been cooled to its freezing point and has been solidified, it has been found that the solid phase remains sticky unless it is subcooled as indicated. Therefore, subcooling about 200 C. below the melting point before removal from the metal surface assures that the thin sheets or flakes will not gum up or stick together in subsequent handling. In addition to preventing adhering of the alloy particles to one another, operating with the preferred parting temperature accomplishes an automatic loosening'of the solidified alloy layer from the metal surface, thereby facilitating the separation step.

The precise operating conditions of a manufacturing unit. can be varied through a substantial range without affecting adversely the reactive character of the alloy product. For example, the immersion or contact time of the metal surface in the molten alloy supply can be varied in a substantial range according to specific needs. Thus, the immersion period has been varied from about 0.4 second to as high as 19 seconds without detriment to product quality. The preferred immersion times are from 0.5 to 2 seconds. Similarly, the rate of movement of the metal surface through the molten bath can be appreciably varied. As an example of the flexibility with respect to this factor, speeds of from 0.02 to as high as about 0.5 feet per second are quite satisfactory. It is customarily preferred to move the metal surface through the alloy at a rate of from 0.1 to 0.5 feet per second.

The thickness of the alloy product will, of course, be affected by the immersion period and the rate of movement of the metal surface. The most important factor in' this regard is the feed alloy temperature, lower temperatures, approach- 10 ing to within 5 or 10 C. of the solidification temperature-of the alloy, contributing greatly to increases in the alloy thickness.

The mean thickness of the alloy as produced can be altered within wide limits without detriment to the subsequent utilization thereof. In general, the layer of alloy deposited inthe metal surface should have a mean thickness of at least 0.005 inch, but preferably a layer of 0.01 to 0.05 inch mean thickness is produced. It has been discovered that allo-ydeposits below the bottom limit of this range frequently exhibit too strong adherence to the metal surface and cause dimculty in removal therefrom. On the other hand, alloy deposits of from 0.01 to 0.05 inch mean thickness are easily lifted and par-ted from the metal surface,

The alloy can be deposited in relatively thick layers when desired by the appropriate combination of factors. Thus, an alloy layer of approximately 0.12 inch mean thickness is produced with an immersion period of 18 to 19 seconds and with an alloy supply maintained about 5 to 10 C. above its melting point. Although this relatively thick alloy exhibits the desired high reactivity in subsequent alkylation treatment, its manufacture is ordinarily avoided. It has been found that the capacity of a given manufacturing unit is decreased rather than increased upon producing such a relatively thick alloy, owing to the relatively long immersion period used. In addition, maintaining the alloy supply at a temperature only slightly above the solidification temperature requires more precise control than desired for large scale operations. The thickness of the alloyproduct is thus preferably maintained in the aforementioned range of 0.01 to 0.05 inch, although these proportions are not extremely critical with respect to the reactivity thereof.

. The pressure of alkylation is maintained sulficiently high to'insure that the alkylating agent will remain predominantly in the liquid phase, a pressure of 50 to pounds per square inch ordinarily being employed. With respect to residence time, it is evident from the'examples heretofore given that the significant improvements are realized in a continuous process employing a residence time of the order of five to ten minutes. In general, the preferred residence time for carrying out the reaction is from five to thirty minutes, representing a substantial improvement over the prior practice of providing a residence time of three hours or more. No specific proportions of liquid alkylating agent to sodium-lead alloy are critical, provided that the alkylating agent is used in excess of the theoretical requirement. However, in most instances, a substantial excess is desirable to insure adequate dispersion of the reacting solids and to facilitate discharge of the reaction products. In the case of ethylation of a sodium-lead alloy with ethyl chloride, the preferred ratio is from 2 to 30 parts of ethyl chloride to 1 part of lead.

Having fully described the invention and the preferred manner of operation thereof, what I claim is:

1. An essentially monosodium alloy of sodium and lead in the form of thin flakes predominating in flakes having a maximum dimension in the range of about /8 to inch, one surface of such flakes comprising substantially all projecting natural crystal faces of identifiable crystals whose axial dimensions are from about 10 to about 50 per cent of the mean thickness of the flake.

2. An essentially monosodium alloy of sodium and lead in the form of flakes of from 0.01 to 0.05 inch mean thickness, predominating in flakes having a maximum dimension in the range of about to inch, one surface thereof comprising substantially all projecting natural faces of crystals whose axial dimension is from 10 to 50 per cent of the mean thickness of the alloy.

3. A process for preparation of a super-reactive alloy of sodium and lead comprising depositing a thin layer of molten approximately monosodiumlead alloy on a single rotatable metal surface Wettable with said alloy, retaining and solidifying the deposited alloy thereon in a quiescent state while cooling by removal of heat essentially only through the metal surface, the cooling being for a period of 1 to 6 seconds to a temperature approximately 200 0. below the solidification temperature of the alloy, then parting the alloy from the metal surface and comminuting to flakes having a maximum dimension in the range of about to 4 inch.

4. A process for preparation of a super-reactive alloy of sodium and lead comprising depositing a layer of molten approximately monosodium lead alloy of from about 0.01 to 0.05 inch in mean thickness on a single rotatable cuprous metal surface by contacting said surface with a molten supply of said alloy for a time of 0.5 to 2.0 seconds, retaining the alloy on the metal surface in a quiescent state while cooling by removal of heat essentially only through the metal surface, the cooling being for a period of 1 to 6 seconds to a temperature of from 150 to 200 C., then parting the alloy from the metal surface and comminuting to flakes having a maximum dimension in the range of about A; to A inch.

5. Process for the manufacture of a tetraalkyllead comprising alkylating an alloy consisting essentially of sodium and lead, said alloy being in the form of flakes having at least one surface comprising predominantly the projecting natural faces of identifiable crystals projecting from a common base.

6. Process for the manufacture of tetraethyllead comprising reacting ethyl chloride with an essentially monosodium-lead alloy, said alloy being in the form of flakes of from 0.01 to 0.05 inch mean thickness and about A; to inch in average size, the flakes having at least one surface comprising predominantly rojecting natural faces of identifiable octahedral shaped crystals projecting from a common base.

'7. Process for the manufacture of tetraethyllead comprising ethylating an essentially monosodium-lead alloy, said alloy being in the form of flakes of from 0.01 to 0.05 inch mean thickness and about A; to 4 inch in average size, the flakes having at least one surface comprising predominantly projecting natural faces of identifiable octahedral shaped crystals projecting from a common base, with liquid ethyl chloride, at a temperature of from to C.

8. Process for the manufacture of tetraethyllead comprising first forming an essentially monosodium alloy of sodium and lead in the form of thin flakes characterized by having at least one surface predominantly comprising projecting natural faces of identifiable octahedral shaped crystals, then ethylating said flakes with an excess of liquid ethyl chloride in th ratio of ethyl chloride to lead between about 2 to 1' and 30 to 1, for a residence time between 5 and 30 minutes and at a temperature between about 70 C. and 100 C.

HOMER M. TANNER.

References Cited in the file of this patent UNITED STATES PATENTS Pyk July 24, 

1. AN ESSENTIALLY MONOSODIUM ALLOY OF SODIUM AND LEAD IN THE FORM OF THIN FLAKES PREDOMINATING IN FLAKES HAVING A MAXINIUM DIMENSION IN THE RANGE OF ABOUT 1/2 TO 1/4 INCH, ONE SURFACE OF SUCH FLAKES COMPRISING SUBSTANTIALLY ALL PROJECTING NATURAL CRYSTAL FACES OF IDENTIFIABLE CRYSTALS WHOSE AZIAL DIMENSIONS ARE FROM ABOUT 10 TO ABOUT 50 PER CENT OF THE MEAN THICKNESS OF THE FLAKE.
 5. PROCESS FOR THE MANUFACTURE OF A TETRAALKYLLEAD COMPRISING ALKYLATING AN ALLOY CONSISTING ESSENTIALLY OF SODIUM AND LEAD, SAID ALLOY BEING IN THE FORM OF FLAKES HAVING AT LEAST ONE SURFACE COMPRISING PREDOMINANTLY THE PROJECTING NATURAL FACES OF IDENTIFIABLE CRYSTALS PROJECTING FROM A COMMON BASE. 